Japanese modern architecture, Sunburst Building

Many interesting modern Japanese buildings are almost unknown outside Japan, mainly because they are located beyond the tourist routes. Here is one of them, located in Tokyo, relatively close to the Yebisu Garden Place, across the train lines (photographed here from the bridge nearby the Tokyo Metropolitan Museum of Photography).

Built in 1996, the building was designed by the Taro Ashihara architects and houses a driving school and classrooms for the bus company Hinomaru Jidosha Group... The architecture is probably inspired by the name of the company, Hinomaru meaning "the circle of sun" and the name of the building is also suggestive: the Sunburst Building. I wonder what's inside the sphere?